This invention relates generally to the field of radio frequency (RF) test and measurement systems, and more specifically to the electrical and software components useful for test and measurement within RF enclosures.
RF enclosures may be used in a variety of test and measurement applications when the amount of RF radiation that impacts a device under test (DUT) must be carefully controlled. Specific examples include prototype testing and production testing of cellular telephones, portable computers, pagers, and other small electronic devices. Often RF enclosures are used in automated or semi-automated environments in which machines are used to place the DUT inside the RF enclosure. In these types of test environments, it is desirable to be able to evaluate the functionality and correct operation of the DUT while the DUT is within the RF enclosure. The use of electronics circuitry and software may be used to apply specific test resources to the DUT and measure the responses. In most applications, the electronics circuitry and software is located both internal and external to the RF enclosure. However, placing high speed electronics within the RF enclosure reduces the RF isolation and therefore degrades the testing accuracy. The proximity of the RF electronics to the DUT also influences the measurement accuracy. Thus, in test and measurement situations involving RF devices there are often two competing design considerations: Including more sophisticated electronic components within an RF enclosure allows more accurate and more comprehensive test procedures to be executed. However from the point of view of RF isolation and noise reduction, fewer electronics components creates smaller amounts of spurious RF energy which leads to improved RF measurements. These competing considerations must both be addressed when designing RF test and measurement systems that incorporate RF enclosures.
Referring now to FIG. 1, a block diagram of RF electronics and software suitable for testing RF devices within an RF enclosure is shown, according to the prior art. A system controller 110 is coupled to a fixture controller 130 in order to send to RF device 150 and receive information from RF device 150. It should be noted that in general, fixture controller 130 is operable to have functionality internal and external to RF enclosure 120. Fixture controller 130 interacts with custom electronics and software 140 to generate test inputs and receive test outputs from the RF device 150. RF device 150 may be coupled directly to the custom electronics 140 or may also be coupled to a nest 160 that is then coupled to custom electronics 140. Nest 160 is often used as the point of attachment for RF device 150, and is operable to provide sensors that measure the state of RF device 150.
It should be noted that the structure of FIG. 1 is representative of the type of fixture system functionality that is currently implemented, although other approaches can be used. The use of custom electronics within the RF enclosure limits the applicability of the RF test system to types of RF devices with different test requirements. Often a particular RF test system is designed to test a particular RF device. So, when a new RF device product line is introduced, a new RF test system must be created. Also, the use of fixture control functionality internal and external to the RF enclosure may be unnecessary, provided that the control functionality external to the RF enclosure can perform the equivalent tasks. An additional issue with the RF test systems currently used is the location of the electronics within the RF enclosure. Ideally, the electronics should be located as close to the RF device under test as possible, since this improves the measurement accuracy. It is also desirable for this circuitry to keep the number of data lines leaving the RF enclosure to a minimum. In many of the current RF test systems, emphasis is placed upon providing the desired measurement functionality. This goal is attained at the expense of providing optimal location of test electronics.
A very important aspect of RF fixture design is the association of information that is unique to the RF device as it relates to the RF fixturing system and the overall test process. This association is particularly important as RF fixturing systems are shared across multiple RF device test plans, as well as, individual fixtures for a particular RF device. This information often consists of test equipment identification, test path calibration constants, and configuration management data required for the test process. Existing solutions for integrating product specific test information into the test process range from very simple hard-coded schemes that are embedded right into the test plan to highly sophisticated database oriented solutions. Each scheme has its unique advantages and disadvantages. The most simplistic solutions lack the flexibility to support multiple unique RF devices, while the more advanced solutions require centralized network connections to be available and are often very expensive.
Thus, there is an unmet need in the art for a RF fixturing system that minimizes the amount of electronics circuitry required within the RF enclosure, that is applicable to a number of RF devices, that places the RF electronics as close to the measurement location as possible, that reduces the number of data lines entering the RF enclosure, and that allows product-specific test information to be stored and retrieved within the RF fixturing system in a convenient, configurable and cost-effective manner.
The RF fixturing system of the present invention allows a plethora of RF devices to be tested using a standard configuration of electronics components of an RF test fixture in combination with device-specific resources resident on one or more electronic customizations or nests. Testing different RF devices can be accomplished by changing the type of customization or nest that is inserted within the RF enclosure. The system thus contains at least an RF test fixture having a standard set of electronics, a nest operable to receive an RF device to be tested in the RF test fixture, and an interface element operable as an interface between the standard set of electronics of the RF test fixture and the RF device. The functionality of the nest that is specific to the RF device within the nest and the functionality of the standard set of electronics work in combination to facilitate testing of the RF device. Different RF devices may be easily tested by substituting different nest having functionality directed more to one or more RF devices to be tested within the RF test fixture.
Depending upon the test and measurement requirements, multiple nests may be present within the RF fixturing system. A RF device is coupled to the nest within the RF enclosure. The nest contains specific features that allow the particular RF device within the nest to be properly tested or evaluated. One of the features located on the nest is a non-volatile memory device. This memory device may be used to store and retrieve product-specific test information, such as nest information, calibration information, test algorithms, operational programs, and other information relevant to the test process. This collection of information may be nest-specific and can be changed depending upon the type of RF device under test. Placing this information in non-volatile memory within the nest allows RF device-specific information to be stored close to the RF device, modified easily, and retrieved easily during a test process.
The nest or xe2x80x9ccustomizationxe2x80x9d is coupled to a nest interface component that serves as the interface between a standard set of resources located within the RF enclosure and the RF device. The standard set of electronics within the RF test fixture provides the electronic resources, preferably at the correct physical location within the fixture, to test a wide array of test devices without requiring customization of test electronics for each device to be tested. Through proper physical partitioning, proper sizing of the number of electronic resources, and by providing the required (or at least most widely used) types of electronic resources, the present invention makes adapting an RF test fixture to test various RF devices faster to implement, better performing and more general purpose. The present invention provides a standard set of requirements/resources for the implementation of many common types of customizations and thus provides for the rapid replacement of such customizations in order to facilitate RF test fixture testing.
The standard set of electronics within the RF test fixture may be any desired functionality. In the test and measurement of RF devices, however, specific resources that may be included within this standard set of electronics may include, but are not limited to, the following: analog signal measurement and generation functionality like DMM multiplexers and voltage reference generators; digital inputs and outputs, including triggering; audio inputs and outputs including transducers and the associated interface and signal conditioning electronics; general purpose switching and signal routing; and communication signal conditioning like level-shifting. Other specific available resources might include: audio path amplifiers/filters/multiplexers for speakers, microphones, and vibration sensors; serial communications transceivers with programmable level shifting capabilities; programmable EEPROM for fixture identification, calibration data, and control program storage; standard interface and location for addition of DUT-specific customization/communication electronics; programmable analog and digital input/output signal lines for interfacing with and control of the DUT; general-purpose relay switches of Form-A and Form-C types for customizable signal routing; digital signal control bus that allows programmable control of all internal test resources; sensor read-back circuitry that allows detection of changes in the position or presence of physical elements inside the fixture; temperature sensor to indicate temperature inside the RF enclosed portion of the fixture; trigger signal multiplexers and signal conditioning, power delivery and sensing functionality for the DUT; and pneumatic switch controller electronics.
The judicious use of analog multiplexing within the RF chamber, in addition to the high degree of digital signal compression obtained using the digital multiplexing over a serial bus, results in reducing the number of signals that are required to traverse the RF barrier. Examples of such analog multiplexing include the audio multiplexing of the source and measurement channels, DMM measurement channel multiplexing, and trigger multiplexing. Such switching allows a large number of test and measurement resources to be provided to the DUT without compromising the RF integrity or signal fidelity of the test system.
The nest interface provides a medium for a variety of sensors and input signals to be applied to an RF device under test (DUT). Often the DUT is placed between an upper nest and a lower nest. Each nest contains specific test and measurement functionality that allows test signals to be applied to the DUT in specific locations. As an example, a cellular telephone contains a speaker that may be more easily tested using a lower nest interface sensor, while the cellular telephone may also contain a microphone that is most easily tested using an upper nest sensor. The provision of more than one nest allows test measurement functionality to be located as close to the measurement location as possible.
Either the upper nest or the lower nest may be coupled to a nest interface component. The nest interface component allows the fixturing system to create test inputs to be applied to the DUT and retrieve test results from the upper nest or the lower nest. The nest interface component allows a wide range of test inputs to be created and applied to the DUT via the nest components. The nest interface component also contains functionality sufficient for receiving the test results from the upper nest or lower nest and processing the results for transmission to a system controller. The location of the nest interface component minimizes the amount of information that needs to be transferred out of the RF enclosure. Thus, the location of the nest interface component effectively increases the RF isolation of the RF enclosure. The nest interface component communicates with electronics components external to the RF enclosure via a fixture interface component.
The fixture interface component provides external RF fixture components a gateway to the electronics components internal to the RF enclosure. The fixture interface component receives information from an external controller via a filtered connector and contains sufficient processing functionality to interpret these commands and interact with the nest interface component, the upper nest and lower nest to achieve test and measurement objectives. The fixture interface component also contains sufficient functionality to format and transmit test results from components internal to the RF enclosure to the external controller. The external controller interacts with the fixture interface to send and receive test specific information as well as diagnostic information and system level commands. System-level commands include commands to change the state of the RF enclosure as well as commands to change the state of the DUT. A system controller, external to the fixturing device, is operable to collect and process test information related to the DUT. The system controller is coupled to the fixturing device via the fixture controller.
The location of the controller functionality external to the RF enclosure reduces the amount of spurious RF emanations and reduces the complexity of the electronics within the RF enclosure. The placement of the fixture interface separate from the DUT reduces the number of data bus lines that are required within the RF enclosure and also reduces the RF emissions within the RF enclosure.